CVT hydromechanical drives of tractors in the 100-150 HP range pose size problems, the solution to which is becoming increasingly pressing. This type of application normally features either a so-called “in-line” hydrostatic unit, in which the axes of the hydraulic pump and hydraulic motor forming part of the hydrostatic unit form an extension one of the other, or a hydrostatic unit, in which the pump and motor axes are parallel, and the pump and motor are connected by transverse hydraulic lines.
An example of this solution is described in U.S. Pat. No. 6,440,026 (Deere). In the Deere patent, a first gear, fitted to a propeller shaft from an engine, meshes with a gear rotating the pump shaft. The pump in turn provides for hydraulically driving a hydraulic motor (also forming part of the hydrostatic unit) which acts on an epicyclic unit via a gear. The hydrostatic units employed in this type of application are therefore extremely bulky crosswise, mainly on account of the two transmission gears.
A need is therefore felt for solutions which reduce the number of gears connecting the hydrostatic unit to the rest of the drive, and which minimize the transverse size of the hydrostatic unit.